The present invention relates to an electrodeless discharge lamp, in particular, a self-ballasted electrodeless discharge lamp.
In recent years, maintenance-free electrodeless discharge lamps (hereinafter, referred to as xe2x80x9celectrodeless fluorescent lampsxe2x80x9d) having a long life that is provided with a phosphor layer inside the lamp have been put to practical use and been under development. Lamps of this type are not provided with electrodes inside the discharge vessel, and discharge occurs in the following manner: a luminous material in the discharge vessel is electromagnetically coupled by high frequency electromagnetic field generating means for generating an electromagnetic field inside the discharge vessel enclosing the luminous material so that a closed loop discharge is formed. The ultraviolet rays that are generated by this discharge are converted to visible light by the phosphor applied onto the inner surface of the discharge vessel. In general, the high frequency electromagnetic field generating means is, for example, an exciting coil through which a high frequency current flows.
Since electrodeless fluorescent lamps include no electrodes inside the discharge vessel, they operate regardless of depletion of an emissive material applied onto electrodes on which the life of a fluorescent lamp depends. Therefore, the electrodeless fluorescent lamps are characterized by having a long life.
Conventionally, in the electrodeless fluorescent lamps, a heat-resistant adhesive such as silicone is poured into a portion where a discharge vessel is in contact with a case for housing a high frequency power connected to an exciting coil to secure the discharge vessel to the case. This method is used, especially for self-ballasted fluorescent lamps with electrodes having a life of about 6000 hours.
However, this method causes detachment of the adhesive because of the contraction of the adhesive due to the heat of the discharge vessel or decrease of the adhesion strength between the discharge vessel and the case due to the degradation or change in quality of the adhesive over time. In particular, since the electrodeless fluorescent lamps have long lives, the decrease of the adhesion strength is particularly problematic.
In order to solve these problems, Japanese Laid-Open Patent Publication No. 9-320541 discloses a technique for compensating for the decrease of the adhesion strength by providing a recess or a protrusion that is engaged with each other in a case and a discharge vessel in a portion in which the case including a ballast is in contact with the discharge vessel.
FIGS. 10A and 10B show the electrodeless fluorescent lamp disclosed in the above publication. FIG. 10A is a cross-sectional view of the entire electrodeless discharge lamp, and FIG. 10B is an enlarged view of the portion where the case is in contract with the discharge vessel. In the drawing, reference numeral 101 denotes a discharge vessel, 102 denotes a phosphor, 303 denotes a translucent conductive film, 304 denotes a regular incandescent lamp base, 305 denotes a blast, 306 denotes ferrite, 307 denotes an exciting coil, 308 is a case cover, 309 denotes a protrusion and 210 denotes a recess.
In the method of engaging the discharge vessel to the case with the recess and the protrusion as shown in FIGS. 10A and 10B, the discharge vessel and the case are engaged with each other directly, so that it is necessary that the discharge vessel matches the shape of the case. On the other hand, the size of the case is determined by the magnitude of the high frequency power to be housed. Thus, the degree of freedom in the design of the shape of the discharge vessel that affects the discharge characteristics significantly may be restricted by the size of the case.
Furthermore, in the above method, there is nothing between the discharge vessel and the high frequency power enclosed in the case, visible light generated in the discharge vessel leaks to the high frequency power or the inside of the case, so that the ratio of the light that can be utilized for effective illumination of an object with respect to the light generated in the discharge vessel (hereinafter, referred to as xe2x80x9clight utilization efficiencyxe2x80x9d) is insufficient and the light utilization efficiency is low.
Therefore, with the foregoing in mind, it is a main object of the present invention to provide an electrode discharge lamp in which the decrease of the adhesion strength between the discharge vessel and the case is suppressed. It is another object to provide an electrodeless discharge lamp in which the light utilization efficiency is improved.
A first self-ballasted electrodeless discharge lamp of the present invention includes a discharge vessel having a cavity, an induction coil that is inserted into the cavity, a ballast for supplying power to the induction coil, a case for covering the ballast; and a lamp base provided in the case. The discharge vessel is secured to the case via a holder. A part of the discharge vessel and a first portion of the holder are engaged with each other to constitute a combination structure. A second portion of the holder and a part of the case are engaged with each other to constitute a combination structure.
It is preferable that at least a part of the holder on the side of the discharge, vessel has a function of reflecting light from the discharge vessel.
It is preferable that at least a part of the holder has a function of shielding a magnetic field from the discharge vessel.
A second self-ballasted electrodeless discharge lamp of the present invention includes a discharge vessel having a cavity, an induction coil that is inserted into the cavity, a ballast for supplying power to the induction coil, a case for covering the ballast, and a lamp base provided in the case. The discharge vessel is secured to the case via a holder. The induction coil includes a core and a winding. The holder has a cylindrical bobbin portion whose surface is wound with the winding and into which the core is inserted. A part of the discharge vessel and a first portion of the holder are engaged with each other to constitute a combination structure. A second portion of the holder and a part of the case are engaged with each other to constitute a combination structure.
In one preferable embodiment, a first end of the core is positioned in the case, and a heat sink is provided in the first end of the core.
A third self-ballasted electrodeless discharge lamp of the present invention includes a discharge lamp having a cavity, an induction coil that is inserted into the cavity, a ballast for supplying power to the induction coil, a case for covering the ballast, and a lamp base provided in the case. The discharge vessel is secured to the case via a holder. A part of the discharge vessel and a first portion of the holder are engaged with each other to constitute a combination structure. A second portion of the holder and a part of the case are engaged with each other to constitute a combination structure. The holder has a circuit holder portion on which the ballast is placed.
In one preferable embodiment, the induction coil includes a core and a winding. The holder has a cylindrical bobbin portion whose surface is wound with the winding and into which the core is inserted. A first end of the core is positioned in the case, and a heat sink is provided in the first end of the core.
In one preferable embodiment, the part of the discharge vessel is a protrusion extending to a second direction substantially perpendicular to a first direction, the induction coil being inserted in the first direction. The first portion of the holder is a recess that clamps the protrusion and has a substantially U-shaped cross section. A notched portion having a size that allows the protrusion to move in a direction substantially perpendicular to the second direction is provided in a periphery of the recess of the holder. The holder has an engagement structure that allows the protrusion to be engaged with the recess by inserting the protrusion of the discharge vessel to the notched portion of the holder, and then rotating the discharge vessel around a portion into which the induction coil is inserted.
In one preferable embodiment, the second portion of the holder is a protrusion. A part of the case is a wedge shaped portion that supports the protrusion after the protrusion of the holder is inserted to a direction opposite to the discharge vessel.
An electrodeless discharge lamp of the present invention includes a discharge vessel having a first shape in which a luminous material is enclosed, high frequency electromagnetic field generating means for generating discharge inside the discharge vessel, a holder having a second shape and a third shape, and a case having a fourth shape. The electrodeless fluorescent lamp has a structure in which the first shape and the second shape are engaged, and a structure in which the third shape and the fourth shape are engaged.
In one preferable embodiment, the holder has at least one function selected from the group consisting of a function of reflecting light from the holder and a function of shielding a magnetic field from the discharge vessel.
In one preferable embodiment, the second shape is a wedge-like shape having elasticity.
In one preferable embodiment, the second shape is a threading groove structure.
In one preferable embodiment, at least one of the third shape and the fourth shape is a wedge-like shape having elasticity.
In one preferable embodiment, at least one of the third shape and the fourth shape is a threading groove structure.
The holder may be constituted with at least two parts.
According to the present invention, the discharge vessel is secured to the case via the holder, and the present invention has a combination structure in which a part of the discharge vessel and the first portion are engaged with each other, and the second portion of the holder and a part of the case are engaged with each other. Therefore, the decrease in the adhesion strength between the discharge vessel and the case can be suppressed.